The basic game of 24 is generations old. It has been played in Asian countries, in particular China, since at least the mid-20th century. There, it was usually played with regular playing (poker) cards and using numbers from 1 (aces) through 13 (kings). Robert Sun created a variant of the game that used specialized cards with four numbers per card, each of which is guaranteed to have a solution. He also created other variations and markets it in the USA with his company Suntex (http://www.24game.com/) as a teaching tool and for competition among elementary school students. Their website begins the description of the game as follows:

"In 1988, successful inventor Robert Sun embarked on a journey to teach children the relationship between numbers through a game. The result of his efforts was the 24® game, a unique mathematics teaching tool that has proven to successfully engage students in grades 1 through 9 ..."

Mathematically, the game comes out of number theory, specifically the theory of "abundant numbers". An abundant number is one for which the sum of its divisors are greater than the number itself. So, Σ divisors(24) = 2+3+4+6+8+12 = 35. This makes 24 a great candidate for this game (although 12, 36, and 48 might be reasonable alternatives). More details on abundant numbers can be found on mathworld.

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